When user equipment (User Equipment, UE for short) is powered on or roams, a top priority is to select a public land mobile network (Public Land Mobile Network, PLMN for short) and successfully register with the public land mobile network. Only in this way, the UE can obtain a communication service, such as a call, and data transmission. After the UE is powered on, the UE first attempts to register with a public land mobile network successfully and previously registered (Registered PLMN, RPLMN for short) by the UE. If the registration fails, the UE proceeds with PLMN search and PLMN selection processes, where in the PLMN search process, the UE searches for an available network according to a frequency band and a radio access technology (Radio Access Technologies, RAT for short) that are supported by the UE, and then forms an available network list. Each element in the list includes a PLMN and a RAT of an available network.
In the PLMN selection process, to help the UE register with an available network more quickly, the UE selects a PLMN according to a particular rule. It is defined in a 3GPP protocol that the UE selects a PLMN according to the following sequence: a home public land mobile network (Home PLMN, HPLMN for short)→a user controlled public land mobile network (User PLMN, UPLMN for short)→an operator controlled public land mobile network (Operator PLMN, OPLMN for short)→other available PLMNs (OTHER Available PLMN). For example, the UE sets priorities for available networks in a found available network list according to signal quality of the HPLMN, UPLMN, OPLMN, and the other available PLMNs, and sorts the available networks in descending order of the priorities. The UE successively selects, in descending order of the priorities, the available networks to attempt to register with until the registration is successful.
For each selected available network, a registration process performed by the UE may involve multiple rounds of signaling message exchange in an entire network. In addition, when a registration attempt fails, the UE further needs to continue to attempt to register with a same available network until a preset stop condition is met, for example, registration attempts reach a preset threshold of failed registration attempts. Therefore, a delay for attempting to register with an available network by the UE is relatively large. In addition, in a roaming scenario of the UE, if there are a large quantity of operators in a roaming area of the UE, the available network list may be long, for example, in Hong Kong, the United States, and some European countries, there are many small operators, and there may be up to dozens of elements (PLMN, RAT) in the available network list.
In the prior art, when initially accessing a network from a roaming area, UE can successfully register with a network in the roaming area after a relatively long time, which affects user experience.